Influence Mechanism of Shield Foam Agent on Soil Physicochemical Properties and Microbial Community

To assess the impact of shield tunnelling foaming agents on soil ecosystems, soil samples collected from shield tunnelling construction sites were used in this study. Laboratory incubation experiments were conducted to investigate changes in soil pH, electrical conductivity (EC), catalase (CAT), β-glucosidase (BG) activity, and microbial community structure under different concentrations of shield tunnelling foaming agents. The results showed that, following treatment with the shield tunnelling foaming agent, soil pH exhibited an overall downward trend, whereas EC gradually increased with prolonged incubation time; both parameters demonstrated a clear time-concentration response relationship. CAT and BG activities were significantly inhibited, with the inhibitory effect increasing as agent concentration increased. High-throughput sequencing results indicated that the shield tunnelling foaming agent significantly restructured the soil microbial community; the relative abundance of the genus Pseudomonas increased, whereas that of Actinobacteriota-related groups decreased; some sensitive fungal groups were inhibited, whereas tolerant fungal groups became enriched. Correlation analysis revealed that soil pH and electrical conductivity (EC) were significantly correlated with enzyme activity and the abundance of dominant microbial groups, suggesting that they are key factors driving changes in community structure. The study indicates that shield tunnelling foaming agents may exert adverse effects on soil ecological functions by altering the physicochemical environment, inhibiting soil enzyme activity, and disrupting microbial community structure. This research provides a scientific basis for the prevention and control of environmental risks associated with waste soil from shield tunnelling construction, as well as for the optimization of more environmentally friendly foaming agents.